The invention relates to a hydraulically operated lift system wherein a hydraulic accumulator is gas-pressurized to provide a counterweight function, thus imposing reduced power requirements on the hydraulic part of the system.
Rosman pending patent application Ser. Nos. 570,590 and 601,481 disclose such systems wherein the accumulator pressurizes a fixed volume of hydraulic fluid which is essentially self-contained at all times in the included volume of (a) the hydraulic end of the accumulator, (b) the actuating end of a lift-operating traction cylinder, and (c) their interconnection, which interconnection includes a so-called power integrator. The accumulator pressure is selected to develop a traction-cylinder force which reflects an average-load condition on the lift system. Pressures on opposite sides of the power integrator are thus equal or nearly equal at all times, and the power integrator is primarily a device for selective transfer of hydraulic fluid from (or to) the accumulator or to (or from) the traction cylinder in any given descent (or lift) displacement of the load. A first pilot-operated check valve in the connection of the integrator to the accumulator, and a second pilot-operated check valve in the connection of the integrator to the traction cylinder, are actuated to open whenever the integrator is called upon to control displacement of hydraulic fluid; and when a given load elevation is to be held, pilot pressures are relieved to allow the respective check valves to maintain the currently shared proportion of hydraulic fluid at the accumulator end and at the actuator end of the system.
A point to be observed with respect to an accumulator-balanced system of the character indicated is that actuated displacement of the traction cylinder must always involve displaced hydraulic fluid which is operative over the entire piston area of the traction cylinder. Thus, for a large traction cylinder displacement, there must be a relatively large volumetric displacement of hydraulic fluid.